1. Field of the Invention
This invention relates generally to pumps, and more particularly to pumps powered by the expansion of a gas.
2. Description of the Prior Art
There are a great number of prior art devices which utilize the force of an expanding gas to pump liquids. Usually, the gas used is air and it is expanded by the application of heat energy from a solar or combustion source.
An early solar pump designed by Isaac de Caus in the mid-seventeenth century included a matrix of lenses focused on half filled, sealed tanks of water. As the air within the tanks expanded the water was forced out through pipes. In the mid-nineteenth century, Mouchot designed a solar pump including a sealed, copper cylinder partially filled with water, and a parabolic reflector for focusing sunlight on the cylinder. As the air expanded the water was forced from the cylinder through a one way check valve.
A more modern example of a solar pump is found in U.S. Pat. No. 3,972,651 of Fletcher. The pump includes a hermetically sealed enclosure 11 floating on a reservoir of water. The enclosure includes a solar heated chamber 48 and a cooling chamber 50 which communicate through a plurality of heat sinks 54. At the bottom of the enclosure 11 there is a sump 20 which is in communication with the reservoir of water via a one way valve 28. When the air in heated chamber 48 expands it will flow through the heat sinks 54 into the cooling chamber and exert pressure on the water in sump 20 to force it up a conduit 34 to an output flume 42. Fletcher's device is metered by a tipple 60 which is filled by dribbles of water from the flume. When the tipple 60 is filled with water it will tip over, raising a `displacer` 44 which separates the chambers 48 and 50. This cools the air within the enclosure and causes water to flow into the sump through valve 28. When the tipple empties the displacer falls and the cycle is repeated.
Fletcher's device is an example of a closed system solar pump, that is, the same air is used over and over during the expansion and compression cycles and is never vented to the atmosphere. As such, Fletcher's pump has many points of similarity with the Stirling hot air engine, which is a classic example of a closed system heat engine.
A problem with closed system pumps or engines is that their design is complicated by the need for complete pressure integrity, and by the elaborate heat dissipating mechanisms required to cool the air between cycles. For example, most of the complexity in Fletcher's device is found in the displacer and tipple mechanism which cools the air within the enclosure. Similarly, a Stirling hot air engine requires water jackets around the compression cylinder and/or an elaborate array of heat radiating fins.